Look back to my first response. As someone who, unfortunately, often deals with people who will talk for three hours to give me five minutes of useful information, conflation of issues is a problem.
The issues you keep keying in on (the Blacksmith scenario) is not the problem in the OP. It's Mr. Cellphone. Try to untangle what the OP was about.
1. Mr. Cellphone is an issue.
2. Here's this thing that happened. In the end, the players were okay with it, and will probably have a heist.
3. The one person who isn't okay with it is Mr. Cellphone.
What's going on here? The DM is frustrated because the one person who has the least involvement with the group is causing the most problems to the DM. So, you have a scenario when a different player (Mr. Ranger) makes an error. This is something that can be corrected. But Mr. Cellphone, who doesn't get involved in social situations (like dealing with the blacksmith) and doesn't pay attention to things (look, a whole set of armor includes gauntlets with a ring attached) is the one person who is giving the DM grief about all of this.
This has nothing to do with the Blacksmith. It has everything to do with unaddressed resentment toward Mr. Cellphone which is rising to the surface because (in the DM's mind) he is not only the one person causing the problem in this scenario, he should be the last person to complain.
Make more sense now?
Of course, no one has noticed that, since by the third page, we immediately went into who was tricking who, player agency, and DM empowerment. See also, Loki's Law.
1. Absolutely. It should have been an issue from the beginning and discussed the second it was happening in game. "Hey man, we're playing D&D right now. Do you mind putting down the phone while we play?"
2. The players O.K. with it are also the players that are paying attention to the game. They seem to get the sense that the DM has already made his stance and it isn't going to change. They are in the acceptance stage. Just because you accept something doesn't mean you agree with it.
3. Of course he's not. He can't even be bothered to put down the phone. I can't get enough D&D, but work and family and such limit how much I'd like to play. When I do play, I put my phone on silent and don't look at it until a session is over.
The original post seems to clearly say that all of the players were unhappy with how this turned out. If they had intended things to happen as they did, their want for the ring and gauntlets would have never came up. It would be no different than if they were selling a painting or urn for gold. They would never know that the items had value above what they were paid. The fact that they do get upset initially indicates that they had interest in the items and had no intention of selling the items before finding their true worth.
Good on the players who realize this can just be turned into a new adventure and are moving on, but what if they hadn't gotten over it?